Image forming apparatus to set target currents

Abstract

An image forming apparatus includes a control portion that controls, before performing continuous image formation on a plurality of transfer materials, a voltage to be applied to a primary transfer member for primary transfer during the continuous image formation, and a correction unit that corrects the primary transfer voltage during the continuous image formation. The correction unit can perform a first mode for controlling the primary transfer voltage according to a target value determined by the control portion, and a second mode for changing the target value and controlling the primary transfer voltage according to the changed value. The control portion performs the first mode if a detected electric resistance is a first value or lower, or a second value, greater than the first value, or higher, and performs the second mode if the resistance is higher than the first value and lower than the second value.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 an image bearing member configured to bear a toner image thereon; 
 a movable intermediate transfer member configured to temporarily bear the toner image, wherein the toner image is transferred from the image bearing member onto the intermediate transfer member in a transfer portion and then is transferred onto a recording material; 
 a transfer member configured to electrostatically transfer the toner image formed on the image bearing member onto the intermediate transfer member in the transfer portion; 
 a power supply configured to apply a voltage to the transfer member; 
 a detection member configured to detect a current flowing through the transfer member during the application of the voltage to the transfer member; 
 an execution portion configured to execute a test mode during preparatory period before an image forming operation, wherein the execution portion determines a target voltage in the test mode so that an output of the detection member becomes a target current when the toner image to be transferred to the recording material passes through the transfer portion; 
 a setting portion configured to set the target current, based on the target voltage determined in the test mode, 
 (a) to a first current when an absolute value of the target voltage is smaller than or equal to a first voltage, wherein the first current is a constant value regardless of the target voltage, 
 (b) to a second current when the absolute value of the target voltage is larger than or equal to a second voltage which is larger than the first voltage, wherein the second current is a constant value regardless of the target voltage and an absolute value of the second current is smaller than an absolute value of the first current, 
 (c) to a third current when an absolute value of the target voltage is larger than the first voltage and smaller than the second voltage, wherein an absolute value of the third current is smaller than the absolute value of the first current and larger than the absolute value of the second current, and wherein the third current is set so that, when an absolute value of the target voltage is a first value, an absolute value of the third current is smaller than the absolute value of the third current when the absolute value of the target voltage is smaller than the first value. 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein the intermediate transfer member contains an ion conductive agent. 
     
     
       3. The image forming apparatus according to  claim 1 , wherein the intermediate transfer member includes a plurality of layers having a layer on an outer peripheral side with a layer hardness that is lower than a layer hardness of a layer of the plurality of layers on an inner peripheral side. 
     
     
       4. The image forming apparatus according to  claim 1 , wherein, during the test mode and while the target current flows, the execution portion determines a target voltage based on each current detected by the detection member when applied with plural currents. 
     
     
       5. The image forming apparatus according to  claim 1 , further comprising a memory configured to previously store a correspondence relation between the target voltage and the first to third current values,
 wherein the setting portion sets the target current based on a reference result between the target voltage and the memory. 
 
     
     
       6. The image forming apparatus according to  claim 5 , further comprising an environment sensor configured to detect an environmental moisture amount nearby the image forming apparatus,
 wherein the memory previously stores the correspondence relation having correlation with the environmental moisture amount, and 
 wherein the setting portion sets the target current based on the correspondence relation between a detection result of the environment sensor, the target voltage, and the memory. 
 
     
     
       7. The image forming apparatus according to  claim 1 , further comprising an electrostatic cleaning member configured to electrostatically clean a residual toner attached to the intermediate transfer member,
 wherein the electrostatic cleaning member is applied with a voltage having a polarity that is the same polarity as a polarity of a voltage applied to the transfer member. 
 
     
     
       8. The image forming apparatus according to  claim 1 , wherein the intermediate transfer member is an intermediate transfer belt having a rubber layer having ion conductivity. 
     
     
       9. The image forming apparatus according to  claim 8 , wherein, after energizing the intermediate transfer belt with energization so that a value obtained by multiplying (i) an amount of energization per unit area and (ii) cumulative time is 30.0 ampere per square meter (A/m 2 ) in a prescribed polarity, a volume resistivity of the intermediate transfer belt increases by one digit or more in volume resistivity of the intermediate transfer belt as compared to before the intermediate transfer belt is energized. 
     
     
       10. The image forming apparatus according to  claim 8 , wherein the intermediate transfer belt includes a base layer formed by resin, the rubber layer, and a surface layer. 
     
     
       11. The image forming apparatus according to  claim 1 ,
 wherein, in a case where a volume resistivity of the intermediate transfer belt is equal to or less than 1×10 10  ohm centimeter (Ω·cm), the setting portion sets the target current as the first current, and 
 wherein, in a case where the volume resistivity of the intermediate transfer belt is larger than 1×10 12  (Ω·cm), the setting portion sets the targets current as the second current. 
 
     
     
       12. The image forming apparatus according to  claim 1 , further comprising an electrifying member configured to electrify the image bearing member into a predetermined potential,
 wherein the setting portion sets the target current based on the target voltage determined in the test mode and the electric potential of the image bearing member.